A zoom lens device which enables acquisition of different focal distances through use of a single lens device has hitherto been used in an optical product, such as a camera or a projector. For instance, as described in JP-A-11-326734, JP-A-2000-321476 and JP-A-2003-202479, a plurality of lens groups are built in a lens barrel, and the lens groups are moved along the direction of the optical axis, thereby effecting scaling action and focusing.
Each of the lens groups is constituted of at least one lens, and an annular lens support frame for supporting the lens. For example, three bosses are provided upright on an outer periphery of the lens support frame while being radially spaced at uniform angular intervals of 120°, and a columnar cam follower is attached to each of the bosses. The lens barrel is formed from a zoom cam cylinder and a fixed cylinder. A plurality of curved cam grooves into which the cam followers of the respective lens groups are inserted are formed in the zoom cam cylinder, and a plurality of linear cam grooves aligned with the direction of the optical axis are formed in the fixed cylinder. When the zoom cam cylinder is rotated, the cam followers are pressed by the curved cam grooves, whereupon the respective lens groups are moved in the direction of a projecting optical axis along the linear cam grooves of the fixed cylinder.
The zoom cam cylinder and the lens support frame are formed from plastic by means of injection molding or the like. Slight, rather than great, variations arise in positions of a molded article where the cam grooves or the cam followers are to be formed. For these reasons, there sometimes arises a case where lens groups built in the lens barrel become tilted with reference to the projection optical axis, or a case where the center of the lenses comes out of alignment with the projection optical axis. The related-art zoom lens device is subjected to inspection after the lens groups have been incorporated in the lens barrel. In accordance with the result of inspection, the lens groups in the lens barrel are rotated through an angle at which the cam followers are spaced from each other around the projection optical axis; that is, an angle of 120°, thereby changing a combination of the cam grooves and the cam followers. Thus, the tilt of the lens groups with reference to the projection optical axis is adjusted.
However, in the case of the zoom lens device wherein, e.g., three bosses and cam followers are provided upright on the outer periphery of the lens support frame while being radially spaced apart at a uniform angular interval of 120° and wherein the lens support frame is supported by the lens barrel by means of the bosses, the three bosses attached to the lens group must once be removed to rotate the lens group by the amount corresponding to the pitch between the cam followers. In that case, unless the lens group is pressed by a jig or the like, the lens group will fall. For this reason, when the center lens group in the zoom lens device into which three or more lens groups are built is subjected to rotational adjustment, the outer lens groups must be removed from the lens barrel for inserting a jig or the like, thereby deteriorating working efficiency.